Lily sends back unfinished artwork (4)
I believe the answer is:
arum
'lily' is the definition.
(a type of lily)
'sends back unfinished artwork' is the wordplay.
'sends back' shows that the letters should be reversed in order.
'unfinished' means to remove the last letter.
'artwork' becomes 'mural' (I've seen this before).
'mural' with its last letter taken off is 'mura'.
'mura' back-to-front is 'ARUM'.
(Other definitions for arum that I've seen before include "plant with a white spathe" , "genus of plants" , "Eg, cuckoo pint" , "A spirit for a lily" , "Cuckoo-pint" .)